The invention relates to a control device and a method for determining the rotor angle of a synchronous machine, in particular at low speeds of a synchronous machine of an electric drive system of an electrically operated vehicle.
It is expected that, in the future, electronic systems which combine new energy storage technologies with electrical drive technology will be used increasingly both in stationary applications, such as wind energy installations or solar installations, for example, as well as in vehicles, such as hybrid or electric vehicles.
In the regulation of a synchronous machine, for example in an electric drive system of an electrically operated vehicle, knowledge of the relative position of the rotor to the stator of the synchronous machine plays a central role. In order to provide a required torque for a synchronous machine, a rotating electrical field is generated in the stator of the machine which rotates synchronously with the rotor. In order to generate this field, the present angle of the rotor is required for the regulation.
One possibility for determining the rotor angle consists in measuring voltages at the neutral point of the synchronous machine with different phase current constellations in the synchronous machine in order to draw conclusions from this in respect of the present rotor angle.
For example, document WO 2009/136381 A2 discloses a method for determining the rotor angle of a synchronous machine in which, by shifting clock patterns of a pulse-width-modulated phase driving, measurement periods for measuring voltages at the neutral point are optimized.
Document DE 697 01 762 T2 discloses a frequency converter for asynchronous motors which, in order to determine phase currents at a low speed of the motor, replaces individual output voltage vectors of phasor-modulated PWM control signals with a sum of on average equivalent output voltage vectors in order to increase the measurement duration for the phase currents.
Document US 2004/0195995 A1 discloses a phasor modulation method for driving an inverter for a synchronous machine in which PWM drive cycles are modified by extending, in a targeted manner, PWM drive signals for optimizing the rotor position determination.
Chapter 8 in Jenny, F; Wüest, D: “Steuerverfahren für selbstgeführte Stromrichter” [Control methods for self-commutated converters], Vdf Hochschulverlag AG, 1995, pages 152-167 discloses the fundamentals of phasor modulation methods for three-phase voltage generation.